Metallocene-containing polymers have been widely utilized for applications ranging from electrochemical sensors to templates for advanced materials to biomedicines, due to their unique physicochemical properties. Cobaltocenium, an 18-e analogue to extensively studied ferrocene, is a cationic metallocene, which possess superior chemical stability, high redox potential and counter-ion dependent solubility. Thus the integration of cobaltocenium into polymeric materials has great potential applications as cationic polyelectrolytes.
Among the metallocene polymers, ferrocene-containing polymers are the mostly studied. Different from ferrocene (18e), cobaltocene (19e) has one more electron, and it can lose one electron readily to form stable cobaltocenium (18e), isoelectronic with ferrocene. Cobaltocenium polymers are much less explored than ferrocene polymers due to the difficulty in synthesis of cobaltocenium derivatives. Different from ferrocene polymers, cobaltocenium polymers are polyelectrolytes with solubility in polar solvents such as water and dimethylformamide.
However, the preparation of side-chain cobaltocenium-containing polymers is challenging due to the lack of efficient controlled polymerization and facile macromolecular engineering, although a few main-chain cobaltocenium polymers have been synthesized via condensation or ring-opening polymerization. As such, a need exists for methods for the synthesis of cobaltocenium-containing monomers and their corresponding side-chain cobaltocenium-containing polymers.